The following invention relates to an attachment for a chain saw for measuring the length of a piece of wood to be cut.
Chain saws are frequently used to cut a single log or length of wood into a number of predetermined lengths for easier handling or to be used as firewood. When cutting firewood it is sometimes necessary to measure the log within tolerances of an inch. For example, some stoves require 18 inch length firewood while others will accommodate wood having a length of 20 inches or more. Especially when cutting firewood it is important that the cut be made perpendicular to the axis of the log. This is so that the cut pieces may be stood on their ends upright for splitting. If the log is cut at an angle the cut piece will have to be propped up in some complicated fashion to enable it to be split.
In the past various length measuring devices for measuring a cut of wood have been available for use as either integral parts of or attachments to a chain saw. For example in Nelson, U.S. Pat. No. 4,341,018 an angled rod is used as a log gauge. The log gauge of Nelson may be adjusted by sliding it through an attaching piece which clamps the guide to the handle. However, beyond a three- or four-inch adjustment the rod would be completely separated from the attachment or would run into the guide bar or the housing of the saw itself. Another problem with the Nelson device is that it is not easily disassembled, and the guide bar, being an angled bar, is an awkward shape for carrying through the difficult terrain sometimes encountered by loggers.
Another type of measuring instrument is shown in U.S. patents to Chontos, U.S. Pat. No. 4,275,504, and Johansson, U.S. Pat. No. 3,276,490. Both of these patents disclose chain saw attachments which employ an extendable metal tape which may either be fastened to the end of a log or one which rigidly extends to the side having index markings for establishing the proper length to be cut. Both the Johansson and the Chontos devices, however, suffer from the problem that they are not easily detached from the chain saw but must be rigidly attached to the saw housing by screws or nuts and bolts. They are thus not suitable for use as retrofit attachments which may be sold and placed on an existing chain saw. Moreover, these devices provide only a linear measurement of length and provide no help in determining if the cut is perpendicular to the grain of the wood. Both also involve complicated mechanisms which involve a coiled metal tape which is spring loaded which could be subject to jamming if the mechanism became rusty or was dropped in sand or dirt.
Yet another type of measuring gauge uses a telescoping rod which is fastened in some manner to the chain saw housing. Two such devices are shown in Hinrichs, U.S. Pat. No. 4,233,739, and Romancky, U.S. Pat. No. 3,531,670. Both of these devices are simply linear guides for marking a length of wood and provide no means for insuring that the cuts are parallel. Both also require complicated fastening means to attach them to the chain saw housing and are thus not suitable for use as a retrofit attachment which may be easily attached to or detached from an existing chain saw.
Yet another type of measuring device is shown in Debell, U.S. Pat. No. 4,388,762. The Debell device is a relatively complicated mechanism, which in order for it to be attached to a chain saw, assumes the presence of a pair of threaded chain bar mounting studs located at a convenient position.
Thus, all of the above chain saw length measuring attachments suffer from one or more deficiencies such as ease of attachment, simplicity of operation, and accuracy of the cut. What is needed, therefore, is a length measuring attachment for a chain saw which may be easily attached to and disassembled from the chain saw, is inexpensive, rugged and yet provides the accuracy necessary to insure that the cut is made at both the proper length and the proper plane.